Circuit interrupters are electrical components that can be used to break an electrical circuit, interrupting the current flow. A basic example of a circuit interrupter is a switch, which generally consists of two electrical contacts in one of two states; either closed, meaning that the contacts are touching and electricity can flow between them, or open, meaning that the contacts are separated, and no electricity can flow between them. A switch may be directly manipulated by a human to provide a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a light switch.
Another example of a circuit interrupter is a circuit breaker. A circuit breaker may be used, for example, in an electrical panel to limit the electrical current being sent through the electrical wiring. A circuit breaker is designed to protect an electrical circuit from damage caused by an overload or a short circuit. If a fault condition such as a power surge occurs in the electrical wiring, the breaker will trip. This will cause a breaker that was in the “on” position to flip to the “off” position and shut down the electrical power leading from that breaker. When a circuit breaker is tripped, it may prevent a fire from starting on an overloaded circuit; it can also prevent the destruction of the device that is drawing the electricity.
A standard circuit breaker has a terminal connected to a power supply, such as a power line from a power company, and another terminal connected to the circuit that the breaker is intended to protect. Conventionally, these terminals are referred to as the “line” and “load” respectively. The line may sometimes be referred to as the input into the circuit breaker. The load, sometimes referred to as the output, feeds out of the circuit breaker and connects to the electrical components being fed from the circuit breaker.
A circuit breaker may be used to protect an individual device, or a number of devices. For example, an individual protected device, such as a single air conditioner, may be directly connected to a circuit breaker. A circuit breaker may also be used to protect multiple devices by connecting to multiple components through a power wire which terminates at electrical outlets, for example.
A circuit breaker can be used as a replacement for a fuse. Unlike a fuse however, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Fuses perform much the same circuit protection role as circuit breakers. However, circuit breakers may be safer to use in some circumstances than fuses, and may be easier to fix.
For example, in a situation where a fuse blows, interrupting power to a section of a building for example, it may not be apparent which fuse controls the interrupted circuit. In this case, all of the fuses in the electrical panel would need to be inspected to determine which fuse appears burned or spent. This fuse would then need to be removed from the fuse box, and a new fuse would need to be installed.
In this respect, circuit breakers can be much simpler to use than fuses. In a situation where a circuit breaker trips, interrupting power to a section of a building for example, it may be easily apparent which circuit breaker controls the interrupted circuit by looking at the electrical panel and noting which breaker has tripped to the “off” position. This breaker can then be simply flipped to the “on” position and power will resume again.
In general, a typical circuit interrupter has two contacts located inside of a housing. The first contact is stationary, and may be connected to either the line or the load. The second contact is movable with respect to the first contact, such that when the circuit breaker is in the “off” or tripped position, a gap exists between the first and second contact.
A problem with circuit interrupters that operate by separating contacts arises because the energized contacts separate when the circuit breaker is tripped, causing a gap to widen between the contacts while the movable contact moves from the closed position to the open position.
As the contacts begin to separate from the closed position, or approach complete closure from an open position, a very small gap exists between the contacts for a brief time while the contacts are closed or opened. An electric arc may be generated across this gap if the voltage between the contacts is high enough. This is because the breakdown voltage between the contacts is positively related to distance under pressure and voltage conditions in typical applications.
The creation of an arc during switching or tripping the circuit interrupter can result in undesirable side effects which can negatively affect the operation of the circuit interrupter, and which can create a safety hazard.
These effects can have consequences for the operation of the circuit interrupter. One possible consequence is that the arc may short to other objects in the circuit interrupter and/or to surrounding objects, causing damage and presenting a potential fire or electrocution safety hazard.
Another consequence of arcing is that the arc energy damages the contacts, causing some material to escape into the air as fine particulate matter. The debris which has been melted off of the contacts can migrate or be flung into the mechanism of the circuit interrupter, destroying the mechanism or reducing its operational lifespan.
Another effect of arcing stems from the extremely high temperature of the arc (tens of thousands of degrees Celsius) which can crack the surrounding gas molecules creating ozone, carbon monoxide, and other compounds. The arc can also ionize the surrounding gasses, potentially creating alternate conduction paths.
Because of these detrimental effects of arcing, it can be very important to quickly cool and quench the arc to prevent damage to the circuit interrupter.
Various techniques for improved arc quenching are known. For example, U.S. Published Patent Applications No. 2012/0037598 and 2012/0261382, assigned to Carling Technologies, Inc., relate to the use of an electromagnetic field to guide the arc toward an arc splitter.
However, generating an electromagnetic field to move the arc consumes power, and generates heat in the device. In order to avoid this, it has been possible to incorporate a permanent magnet into the circuit interrupter which produces a magnetic field without requiring a supply of current. Even systems that are polarity insensitive have been developed. However, all of these systems focus on a device to draw to guide the arc into an arc quenching device.
Arc quenching devices can be effective in protecting devices, however, they do have lifespans that limit their effectiveness over time. Additionally, elaborate arc quenching systems can add significant cost to the circuit breaker.
Another method for minimizing the development of arcing when contacts are opened or closed in AC systems is to time the opening or closing as near as possible to the zero crossing. However, this method is not available for use in DC systems as there is no zero crossing.
It is therefore desired to provide an alternative system that is usable with a circuit interrupter that overcomes these limitations.